the offspring of an ass, a little burro (see Molina)
(partly a loanword from Spanish, asno, burro)
Alonso de Molina:
axno conetl. burrico. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 10r. col. 2. Thanks to Joe Campbell for providing the transcription.